1. Field of the Invention
The present invention relates to a method for preparating galacto-oligosaccharides in which lactose, or both lactose and galactose are employed as their material(s).
In general, an oligosaccharide that contains galactose in its molecule is called a galacto-oligosaccharide.
2. Description of Prior Art
In the art of preparation of galacto-oligosaccharides, the following methods have been heretofore employed: the one to produce transglycosylated galacto-oligosaccharides to allow an enzyme generated from microorganism to act on lactose (Japanese Patent Publication (Examined) No. 58-20266 and Japanese Patent Publication (Examined) No. 60-25189); the one to use bean oligosaccharides from soybean milk whey (Japanese Patent Publication (Unexamined) No. 62-155082); the one for extraction to use raffinose of beet sugar (Japanese Patent Publication (Unexamined) No. 62-126951); and so on.
A problem exists in the results obtained through the mentioned known methods, however, that they are so low in purity of aimed galacto-oligosaccharides as to be more or less 50%, futher lower in sugar content of them, and not easy to treat because of their liquid state (about 75% in concentration). Therefore, it has been necessary for these conventional methods to additionally conduct a process of extracting galacto-oligosaccharides of higher purity and to purify them by some chromatographic method or the like. The compositions of the conventional galacto-oligosaccharides made known to the public are as shown in the following Table 1.
TABLE 1 ______________________________________ (1) (2) (3) ______________________________________ Tradename Cup-oligo Lacto-oligo- Soybean-oligo- saccharides saccharides Galacto- 48 to 58 36.2 31.5 oligo- saccharide Disaccha- 7 to 10 26.1 44.7 ride Monosaccha- 30 to 40 37.7 ride Other sugars 23.7 ______________________________________ Note: (1) obtained from lactose produced by Nisshin Sugar Refinary; (2) obtained from lactose produced by Yakult; and (3) obtained from soybean produced by Calpis.